The F-35 is descended from the X-35, which was the winning design of the Joint Strike Fighter (JSF) program. It is being designed and built by an aerospace industry team led by Lockheed Martin. Other major F-35 industry partners include Northrop Grumman, Pratt & Whitney and BAE Systems. The F-35 took its first flight on 15 December 2006. The United States plans to buy 2,457 aircraft. The F-35 variants are intended to provide the bulk of the manned tactical airpower of the U.S. Air Force, Navy, and Marine Corps over the coming decades. Deliveries of the F-35 for the U.S. military are scheduled to be completed in 2037.[10]

F-35 JSF development is being principally funded by the United States with additional funding from partners. The partner nations are either NATO members or close U.S. allies. The United Kingdom, Italy, Australia, Canada, Norway, Denmark, the Netherlands, and Turkey are part of the active development program;[11][12]several additional countries have ordered, or are considering ordering, the F-35.

The JSF program was designed to replace the United States military F-16, A-10, F/A-18 (excluding newer E/F "Super Hornet" variants) and AV-8B tactical fighter and attack aircraft. To keep development, production, and operating costs down, a common design was planned in three variants that share 80 percent of their parts:

George Standridge, Vice President of Strategy and Business Development for Lockheed Martin Aeronautics, and a Naval Aviator who flew the F/A-18 Hornet in both the U.S. Navy and the Naval Reserve, predicted in 2006 that the F-35 will be four times more effective than legacy fighters in air-to-air combat, eight times more effective in air-to-ground combat, and three times more effective in reconnaissance and suppression of air defenses – while having better range and requiring less logistics support and having around the same procurement costs (if development costs are ignored) as legacy fighters.[13] The design goals call for the F-35 to be the premier strike aircraft through 2040 and to be second only to the F-22 Raptor in air superiority.[14]

The JSF development contract was signed on 16 November 1996, and the contract for System Development and Demonstration (SDD) was awarded on 26 October 2001 to Lockheed Martin, whose X-35 beat the Boeing X-32. Although both aircraft met or exceeded requirements, the X-35 design was considered to have less risk and more growth potential.[15] The designation of the new fighter as "F-35" is out-of-sequence with standard DoD aircraft numbering,[16] by which it should have been "F-24". It came as a surprise even to the company, which had been referring to the aircraft in-house by this expected designation.[17]

The development of the F-35 is unusual for a fighter aircraft in that no two-seat trainer versions have been built for any of the variants; advanced flight simulators mean that no trainer versions were deemed necessary.[18] Instead F-16s have been used as bridge trainers between the T-38 and the F-35. The T-X was intended to be used to train future F-35 pilots, but this might succumb to budget pressures in the USAF.[19]

Based on wind tunnel testing, Lockheed Martin slightly enlarged its X-35 design into the F-35. The forward fuselage is 5 inches (130 mm) longer to make room for avionics. Correspondingly, the horizontal stabilators were moved 2 inches (51 mm) rearward to retain balance and control. The top surface of the fuselage was raised by 1 inch (25 mm) along the center line. Also, it was decided to increase the size of the F-35B STOVL variant's weapons bay to be common with the other two variants.[15] Manufacturing of parts for the first F-35 prototype airframe began in November 2003.[20] Because the X-35 did not have weapons bays, their addition in the F-35 would cause design changes which would lead to later weight problems.[21][22]

The F-35B STOVL variant was in danger of missing performance requirements in 2004 because it weighed too much; reportedly, by 2,200 lb (1,000 kg) or 8 percent. In response, Lockheed Martin added engine thrust and thinned airframe members; reduced the size of the common weapons bay and vertical stabilizers; re-routed some thrust from the roll-post outlets to the main nozzle; and redesigned the wing-mate joint, portions of the electrical system, and the portion of the aircraft immediately behind the cockpit.[23] Many of the changes were applied to all three variants to maintain high levels of commonality. By September 2004, the weight reduction effort had reduced the aircraft's design weight by 2,700 pounds (1,200 kg),[24] but the redesign cost $6.2 billion and delayed the project by 18 months.[25]

Lockheed Martin Aeronautics is the prime contractor and performs aircraft final assembly, overall system integration, mission system, and provides forward fuselage, wings and flight controls system. Northrop Grumman provides Active Electronically Scanned Array (AESA) radar, electro-optical AN/AAQ-37 Distributed Aperture System (DAS), Communications, Navigation, Identification (CNI), center fuselage, weapons bay, and arrestor gear. BAE Systems provides the Flight Control Software (FCS1), the Electronic warfare systems, crew life support and escape systems, aft fuselage, empennages as well as the horizontal and vertical tails. Alenia will perform final assembly for Italy and, according to an Alenia executive, assembly of all European aircraft with the exception of Turkey and the United Kingdom.[28][29] The F-35 program has seen a great deal of investment in automated production facilities. For example, Handling Specialty produced the wing assembly platforms for Lockheed Martin.[30]

On 19 December 2008, Lockheed Martin rolled out the first weight-optimized F-35A, designated AF-1. It was the first F-35 built at full production speed, and is structurally identical to the production F-35As that were delivered starting in 2010.[31] On 5 January 2009, six F-35s had been built, including AF-1 and AG-1; another 13 pre-production test aircraft and four production aircraft were being manufactured.[32] On 6 April 2009, U.S. Secretary of Defense Robert Gates proposed speeding up production for the U.S. to buy 2,443 F-35s.[33]

The F-35 program has experienced a number of cost overruns and developmental delays. The program's delays have come under fire from the U.S. Congress and some U.S. Department of Defense officials. The program has undergone a number of reassessments and changes since 2006. The Government Accountability Office (GAO) warned in March 2006 that excessive concurrency might result in expensive refits for several hundred F-35 aircraft that are planned for production before design testing is completed.[34] In 2010, acquisition chief Ashton Carter issued an Acquisition Decision Memorandum restructuring the F-35 program.[35] In November 2010, the GAO found that "Managing an extensive, still-maturing global network of suppliers adds another layer of complexity to producing aircraft efficiently and on-time" and that "due to the extensive amount of testing still to be completed, the program could be required to make alterations to its production processes, changes to its supplier base, and costly retrofits to produced and fielded aircraft, if problems are discovered."[36] USAF budget data in 2010, along with other sources, projected the F-35 to have a flyaway cost from US$89 million to US$200 million over the planned production run.[37][38] In February 2011, the Pentagon put a price of $207.6 million on each of the 32 aircraft to be acquired in FY2012, rising to $304.16 million ($9,732.8 million ÷ 32 aircraft) if its share of research, development, test and evaluation (RDT&E) spending is included.[39][40]

On 21 April 2009, media reports, citing Pentagon sources, said that during 2007 and 2008, spies downloaded several terabytes of data related to the F-35's design and electronics systems, potentially compromising the aircraft and aiding the development of defense systems against it.[41] Lockheed Martin rejected suggestions that the project was compromised, stating it "does not believe any classified information had been stolen".[42] Other sources suggested that the incident caused both hardware and software redesigns to be more resistant to cyber attack.[43] In March 2012, BAE Systems was reported to be the target of cyber espionage. BAE Systems refused to comment on the report, although they did state, "[Our] own cyber security capability can detect, prevent and rectify such attacks."[44]

On 9 November 2009, Ashton Carter, under-secretary of defense for acquisition, technology and logistics, acknowledged that the Pentagon "joint estimate team" (JET) had found possible future cost and schedule overruns in the project and that he would be holding meetings to attempt to avoid these.[45] On 1 February 2010, Gates removed the JSF Program Manager, U.S. Marine Corps Major General David Heinz, and withheld $614 million in payments to Lockheed Martin because of program costs and delays.[46][47]

On 11 March 2010, a report from the Government Accountability Office to United States Senate Committee on Armed Services projected the overall unit cost of an F-35A to be $113 million in today's money.[48] In 2010, Pentagon officials disclosed that the F-35 program has exceeded its original cost estimates by more than 50 percent.[49] An internal Pentagon report critical of the JSF project states that "affordability is no longer embraced as a core pillar". In 2010, Lockheed Martin expected to reduce government cost estimates by 20 percent.[50] On 24 March 2010, Gates termed the cost overruns and delays as "unacceptable" in a testimony before the U.S. Congress; and characterized previous cost and schedule estimates as "overly rosy". Gates insisted the F-35 would become "the backbone of U.S. air combat for the next generation" and informed the Congress that he had expanded the development period by an additional 13 months and budgeted $3 billion more for the testing program while slowing down production.[51] In August 2010, Lockheed Martin announced delays in resolving a "wing-at-mate overlap" production problem, which would slow initial production.[52]

In November 2010, as part of a cost-cutting measure, the co-chairs of the National Commission on Fiscal Responsibility and Reform suggested cancelling the F-35B and halving orders of F-35As and F-35Cs.[53][54][55]Air Force Magazine reported that "Pentagon officials" were considering canceling the F-35B because its short range meant that the forward bases or amphibious ships it would operate from would be in range of hostile tactical ballistic missiles.[56] Lockheed Martin consultant Loren B. Thompson said that this rumor was a result of the usual tensions between the U.S. Navy and Marine Corps, and there was no alternative to the F-35B as an AV-8B Harrier II replacement.[57] He also confirmed further delays and cost increases because of technical problems with the aircraft and software, blaming most of the delays and extra costs on redundant flight tests.[58]

In November 2010, the Center for Defense Information estimated that the program would be restructured with an additional year of delay and $5 billion in additional costs.[59] On 5 November 2010, the Block 1 software flew for the first time on BF-4.[60] As of the end of 2010, only 15% of the software remained to be written, but this was reported to include the most difficult sections such as data fusion.[61] In 2011, it was revealed that 50% of the eight million lines of code had been written and that it would take another six years to complete the software to the new schedule.[62] By 2012, the total estimated lines of code for the entire program (onboard and offboard) had grown from 15 million lines to 24 million lines.[63]

In 2011, the program head and Commander of the Naval Air Systems Command, Vice Admiral David Venlet, confirmed that the concurrency built into the program "was a miscalculation".[64] This was during a contract dispute where the Pentagon insisted that Lockheed Martin help cover the costs of applying fixes found during testing to aircraft already produced.[65] Lockheed Martin objected that the cost sharing posed an uninsurable unbounded risk that the company could not cover, and later responded that the "concurrency costs for F-35 continue to reduce".[66][67] The Senate Armed Services Committee strongly backed the Pentagon position.[68] In December 2011, Lockheed Martin accepted a cost sharing agreement.[69] The Aerospace Industries Association warned that such changes would force them to anticipate cost overruns in future contract bids.[70] As of 2012, problems found in flight testing were expected to continue to lead to higher levels of engineering changes through 2019.[71] The total additional cost for concurrency in the program is around $1.3 billion.[72] By the next year the cost had grown to $1.7 billion.[73]

In January 2011, Defense Secretary Robert Gates expressed the Pentagon's frustration with the rising costs of the F-35 program when he said, "The culture of endless money that has taken hold must be replaced by a culture of restraint." Focusing his attention on the troubled F-35B, Gates ordered "a two-year probation", saying it "should be canceled" if corrections are unsuccessful.[74] Gates has stated his support for the program.[75] Some private analysts, such as Richard Aboulafia, of the Teal Group state that the F-35 program is becoming a money pit.[76] Gates' successor, Leon Panetta, ended the F-35B's probation on 20 January 2012, stating "The STOVL variant has made—I believe and all of us believe—sufficient progress."[77]

Former Pentagon manager Paul G. Kaminski has said that the lack of a complete test plan has added five years to the JSF program.[78]Initial operating capability (IOC) will be determined by software development rather than by hardware production or pilot training.[79] As of May 2013[update], the USMC plan an IOC in "mid-2015" for the F-35B with Block 2B software which gives basic air-to-air and air-to-ground capability. It has been reported that the USAF is planning to bring forward IOC for the F-35A to the Block 3I software in mid-2016 rather than waiting for the full-capability Block 3F in mid-2017; the F-35C will not enter service with the USN until mid-2018.[2] The $56.4 billion development project for the aircraft should be completed in 2018 when the Block five configuration is expected to be delivered—several years late and considerably over budget.[80]

Delays in the F-35 program may lead to a "fighter gap" where the United States and other countries will lack sufficient fighters to cover their requirements.[81] Israel may seek to buy second-hand F-15Es,[82] while Australia also sought additional F/A-18 Super Hornets in the face of F-35 delays.[83]

In May 2011, the Pentagon's top weapons buyer Ashton Carter said that its new $133 million unit price was not affordable.[84] In 2011, The Economist warned that the F-35 was in danger of slipping into a "death spiral" where increasing per-aircraft costs would lead to cuts in number of aircraft ordered, leading to further cost increases and further order cuts.[85] Later that year, four aircraft were cut from the fifth Low Rate Initial Production (LRIP) order to pay for cost overruns;[86] in 2012, a further two aircraft were cut.[87] Lockheed Martin acknowledged that the slowing of purchases would increase costs.[88] David Van Buren, U.S. Air Force acquisition chief, said that Lockheed Martin needed to cut infrastructure to match the reduced market for their aircraft.[89] The company said that the slowdown in American orders will free up capacity to meet the urgent short term needs of foreign partners for replacement fighters.[90] Air Force Secretary Michael Donley said that no more money was available and that future price increases would be matched with cuts in the number of aircraft ordered.[91] Later that month, the Pentagon reported that costs had risen another 4.3 percent, partially resulting from production delays.[92] In 2012, the purchase of six out of 31 aircraft was tied to performance metrics of the program.[93] In 2013, Bogdan repeated that no more money was available, but that he hoped to avoid the death spiral.[94] In 2014 it was reported that another eight aircraft would be cut from the next year's order.[95]

Japan has warned that it may halt their purchase if unit costs increase, and Canada has indicated it is not committed to a purchase yet.[96][97] The United States is projected to spend an estimated $323 billion for development and procurement on the program, making it the most expensive defense program ever.[98] Testifying before a Canadian parliamentary committee in 2011, Rear Admiral Arne Røksund of Norway estimated that his country's 52 F-35 fighter jets will cost $769 million each over their operational lifetime.[99] In 2012, the total life-cycle cost for the entire U.S. fleet was estimated at US$1.51 trillion over a 50-year life, or $618 million per plane.[100] To reduce this high life-cycle cost over a 50-year lifetime, the USAF is considering reducing Lockheed Martin's role in Contractor Logistics Support.[101] The company has responded that this cost estimate relies on future costs beyond its control such as USAF reorganizations and yet to be specified upgrades.[102] Delays have negatively affected the program's worldwide supply chain and partner organizations.[103]

In 2012, General Norton A. Schwartz decried the "foolishness" of reliance on computer models to settle the final design of the aircraft before flight testing found the issues that needed redesign.[104] In 2013, JSF project team leader USAF Lieutenant General Chris Bogdan said that "A large amount of concurrency, that is, beginning production long before your design is stable and long before you've found problems in test, creates downstream issues where now you have to go back and retrofit airplanes and make sure the production line has those fixes in them. And that drives complexity and cost".[105] Bogdan praised the improvement in the program ever since Lockheed Martin was forced to assume some of the financial risks.[106]

In 2012, in order to avoid further redesign delays, the U.S. DoD accepted a reduced combat radius for the F-35A and a longer takeoff run for the F-35B.[107][108] The F-35B's estimated radius has also decreased by 15 percent.[109] In a meeting in Sydney in March, the United States pledged to eight partner nations that there would be no more program delays.[110]

In May 2012, Lockheed Martin Chief Executive Bob Stevens complained that the Defense Department's requirements for cost data were driving up program cost.[111] Stevens also admitted that a strike might cause a production shortfall of the target of 29 F-35s that year.[112] Striking workers questioned the standards of replacement workers, as even their own work had been cited for "inattention to production quality" with a 16% rework rate.[113] The workers went on strike to protect pensions whose costs have been the subject of negotiations with the Department of Defense over the next batch of aircraft.[114] These same pension costs were cited by Fitch in their downgrade of the outlook for Lockheed Martin's stock price.[115] Stevens said that while he hoped to bring down program costs, the industrial base was not capable of meeting the government's expectations of affordability.[116][117]

According to a June 2012 Government Accountability Office report, the F-35's unit cost has almost doubled, an increase of 93% over the program's 2001 baseline cost estimates.[118] In 2012, Lockheed Martin reportedly feared that the tighter policies for award fees of the Obama administration would reduce their profits by $500 million over the following five years.[119] This was demonstrated in 2012 when the Pentagon withheld the maximum $47 million allowed for the company's failure to certify its program to track project costs and schedules.[120] The GAO has also faulted the USAF and USN for not fully planning the costs of extending legacy F-16 and F-18 fleets to cover for the delayed F-35.[121] Due to cost cutting measures, the U.S. Government and the GAO have stated that the flyaway cost (including engines) has been dropping. The U.S. Government estimates that in 2020 an "F-35 will cost some $85m each or less than half of the 2009 initial examples cost. Adjusted to today’s dollars the 2020 price would be $75m each."[122]

In 2013, Lockheed Martin began to lay off workers at the Fort Worth plant where the F-35s were assembled.[123] They said that the currently estimated concurrency costs of refitting the 187 aircraft built by the time testing concludes in 2016 are now less than previously feared.[124] The GAO's Michael Sullivan said that the company had failed to get an early start on the systems engineering and had not understood the requirements or the technologies involved at the program's start.[125] The Pentagon vowed to continue funding the program during budget sequestration if possible.[126] The U.S. budget sequestration in 2013 could slow development of critical software,[127] and the Congress has ordered another study to be made on the software development delays.[128] As of 2014, software development remains the "number one technical challenge" for the F-35.[129]

In June 2013, Frank Kendall, Pentagon acquisition, technology and logistics chief, declared "major advances" had been made in the F-35 program over the last three years; and that he intended to approve production rate increases in September. Air Force Lt. Gen. Christopher Bogdan, program executive officer, reported far better communications between government and vendor managers, and that negotiations over Lot 6 and 7 talks were moving fast. It was also stated that operating costs had been better understood since training started, and he predicted "we can make a substantial dent in projections" of operating costs.[130]

In July 2013, further doubt was cast on the latest (long delayed) schedule, with further software delays, and sensor, display and wing buffet problems continuing.[131] In August it was revealed that the Pentagon was weighing cancellation of the program as one possible response to the budget sequestration,[132][133] and the United States Senate Appropriations Subcommittee on Defense voted to cut advanced procurement for the fighter.[134]

On 21 August 2013, C-Span reported that Congressional Quarterly and the Government Accountability Office were indicating the "total estimated program cost now is $400b—nearly twice the initial cost". The current investment was documented as approximately $50 billion. The projected $316 billion cost in development and procurement spending was estimated through 2037 at an average of $12.6 billion per year. These were confirmed by Steve O'Bryan, Vice President of Lockheed Martin on the same date.[135]

In 2013, a RAND study found that during development the three different versions had drifted so far apart from each other that having a single base design might now be more expensive than if the three services had simply built entirely different aircraft tailored to their own requirements.[136]

In 2014, the airframe cost went below $100 million for the first time, and the Air Force expected unit costs to fall.[137]

A 2014 Center for International Policy study cast doubt on the number of indirect jobs created by the program, which has been a key selling point for the F-35 to Congress. Lockheed stood by their job numbers and said that their accounting was in line with industry norms.[138]

A January 2014 report by J. Michael Gilmore said that new software delays could delay Block 2B release by 13 months;[139] this was reduced to 4 months in the DOTE report from November 2014.[140] The F-35 program office considers software to be the top technical risk to the program, and the USMC has maintained their expectation of an IOC in July 2015.[141]

In 2014, U.S. Senator John McCain blamed cost increases in the program on "cronyism".[142]

In 2014, the GAO found that the F-35 fleet would have operating costs 79% higher than the aircraft it replaced.[143] The latest Selected Acquisition Report stated that the program cost has increased 43% from 2001 with Program Acquisition Unit Cost up 68% and Unit Recurring Flyaway up 41%.[7] The F-35A's cost per flying hour is $32.5k while the F-16C/D is $25.5k but each F-35A will only fly 250 hours a year to the F-16's 316 hours resulting in the same yearly operating cost.[7][144]

In July of 2014, Lockheed Martin, Northrop Grumman, and BAE Systems announced they would invest a combined $170M into the program[clarification needed], which is anticipated to save over $10M per aircraft. This initiative has set the project on track for an $80M (including engine) price tag per aircraft (F-35A), by 2018 when full production starts.[145]

Considerable criticism followed in the wake of U.S. Ambassador Tom Schieffer's confirmation to the Joint Standing Committee on Foreign Affairs (JSCFADT) on 21 June 2004: "With regard to the stealth technology, the airplane that Australia will get will be the stealthiest airplane that anybody outside the United States can acquire. We have given assurances to Australia that we will give you the absolute maximum that we can with regard to that technology. Having said that, the airplane will not be exactly the same airplane as the United States will have. But it will be a stealth fighter; it will have stealth capabilities; and it will be at the highest level that anyone in the world has outside the United States."[146][147] Lockheed Martin's Tom Burbage stated in a 2006 article that export of key technologies such as stealth would be limited by U.S. national disclosure policy.[148] A Jane's article in 2004 gave a hint that US$1B, spent on several contracts, may provide for a less stealthy F-35 export configuration.[149]

Andrew Krepinevich has questioned the reliance on "short range" aircraft like the F-35 or F-22 to "manage" China in a future conflict and has suggested reducing the number of F-35s ordered in favor of a longer range platform like the Next-Generation Bomber, but Michael Wynne, then United States Secretary of the Air Force rejected this plan of action in 2007.[150][151] By 2012, Wynne had conceded that America's short ranged fifth-generation fighters would need drop tanks in order to be effective, with resultant compromises to their radar low observable "stealth" characteristics.[152] In 2011, the Center for Strategic and Budgetary Assessments (CSBA) pointed to the restructuring of the F-35 program and the return of the bomber project as a sign of their effectiveness, while Rebecca Grant said that the restructuring was a "vote of confidence" in the F-35 and "there is no other stealthy, survivable new fighter program out there".[153] Lockheed Martin has also said that the F-35 is designed to launch internally carried bombs at supersonic speed and internal missiles at maximum supersonic speed.[154]

In 2008, two former RAND Corporation employees conducted simulated war games in which the Russian Sukhoi Su-35 fighter defeated the F-35 in the Harpoon 3 video game.[155][156] Though it was implicated this was an official study, RAND Corporation refuted having conducted any such study.[157] During a formal briefing by the Australian Department of Defence to the Australian defence minister Joel Fitzgibbon, it was stated that reports of the simulation were inaccurate and did not compare the F-35's flight performance against other aircraft.[158] The Pentagon and Lockheed Martin also stated that these simulations did not address air-to-air combat.[159][160] A Lockheed Martin press release points to USAF simulations regarding the F-35's air-to-air performance against adversaries described as "4th generation" fighters, in which it claims the F-35 is "400 percent" more effective. Major General Charles R. Davis, USAF, the F-35 program executive officer, has stated that the "F-35 enjoys a significant Combat Loss Exchange Ratio advantage over the current and future air-to-air threats, to include Sukhois".[160]

In September 2008, in reference to the original plan to fit the F-35 with only two air-to-air missiles (internally), Major Richard Koch, chief of USAF Air Combat Command’s advanced air dominance branch is reported to have said that "I wake up in a cold sweat at the thought of the F-35 going in with only two air-dominance weapons."[161] The Norwegians have been briefed on a plan to equip the F-35 with six AIM-120D missiles by 2019.[162] Former RAND author John Stillion has written of the F-35A's air-to-air combat performance that it "can't turn, can't climb, can't run"; Lockheed Martin test pilot Jon Beesley has stated that in an air-to-air configuration the F-35 has almost as much thrust as weight and a flight control system that allows it to be fully maneuverable even at a 50-degree angle of attack.[163][164] Consultant to Lockheed Martin Loren B. Thompson has said that the "electronic edge F-35 enjoys over every other tactical aircraft in the world may prove to be more important in future missions than maneuverability".[165]

In an April 2009 interview with the state-run[166]Global Times, Chen Hu, editor-in-chief of World Military Affairs magazine said that the F-35 is too costly because it attempts to provide the capabilities needed for all three American services in a common airframe.[167] U.S. defense specialist Winslow T. Wheeler and aircraft designer Pierre Sprey have commented of the F-35 being "heavy and sluggish" and possessing "pitifully small load for all that money", further criticizing the value for money of the stealth measures as well as lacking fire safety measures; his final conclusion was that any air force would be better off maintaining its fleets of F-16s and F/A-18s compared to buying into the F-35 program.[168] A senior U.S. defense official was quoted as saying that the F-35 will be "the most stealthy, sophisticated and lethal tactical fighter in the sky," and added "Quite simply, the F-15 will be no match for the F-35."[169] After piloting the aircraft, RAF Squadron Leader Steve Long said that, over its existing aircraft, the F-35 will give "the RAF and Navy a quantum leap in airborne capability."[170]

In November 2009, Jon Schreiber, head of F-35 international affairs program for the Pentagon, said that the U.S. will not share the software code for the F-35 with its allies.[171] The US plans to set up a reprogramming facility that will develop JSF software and distribute it to allies.[172]

In 2011, Canadian politicians raised the issue of the safety of the F-35's reliance on a single engine (as opposed to a twin-engine configuration, which provides a backup in case of an engine failure). Canada, and other operators, had previous experience with a high-accident rate with the single-engine Lockheed CF-104 Starfighter with many accidents related to engine failures. Defence Minister Peter MacKay, when asked what would happen if the F-35's single engine fails in the Far North, stated "It won’t".[173]

In November 2011, a Pentagon study team identified the following 13 areas of concern that remained to be addressed in the F-35:[174][175]

In March 2012, Tom Burbage, and Gary Liberson, of Lockheed Martin addressed an Australian Parliamentary Committee about earlier assessments. Liberson stated: "Our current assessment that we speak of is: greater than six to one relative loss exchange ratio against in four versus eight engagement scenarios—four blue [F-35s] versus eight advanced red threats in the 2015 to 2020 time frame." Later stating: "And it is very important to note that our constructive simulations that Mr Burbage talks about without the pilot in the loop are the lowest number that we talk about—the greater than six to one. When we include the pilot in the loop activities, they even do better". Burbage said: "We actually have a fifth-gen airplane flying today. The F-22 has been in many exercises. We have one of the pilots here who flew it and they can tell you that in any real-world event it is much better than the simulations forecast. We have F-35 flying today; it has not been put into that scenario yet, but we have very high quality information on the capability of the sensors and the capability of the airplane, and we have represented the airplane fairly and appropriately in these large-scale campaign models that we are using. But it is not just us...it is our air force; it is your air force; it is all the other participating nations that do this; it is our navy and our marine corps that do these exercises. It is not Lockheed in a closet genning up some sort of result."[176]

In May 2012, Michael Auslin of the American Enterprise Institute has questioned the capability of the F-35 to engage modern air defenses.[177] In July 2012, the Pentagon awarded Lockheed Martin $450 million to improve the F-35 electronic warfare systems and incorporate Israeli systems.[178]

In a negative assessment of the Joint Strike Fighter, the think tank Air Power Australia declared that the Joint Strike Fighter is not designed to perform air superiority roles and also is not adapted to performing the long range penetration strike role filled by previous Australian aircraft like the General Dynamics F-111C. Critically, they also stated that the F-35’s "intended survivability and lethality are mismatched against the operational environment in which the aircraft is intended to be used."[179]

In June 2012, Australia's Air Vice Marshal Osley responded to Air Power Australia's criticisms by saying "Air Power Australia (Kopp and Goon) claim that the F-35 will not be competitive in 2020 and that Air Power Australia's criticisms mainly center around F-35's aerodynamic performance and stealth capabilities." Osley continued with, "these are inconsistent with years of detailed analysis that has been undertaken by Defence, the JSF program office, Lockheed Martin, the U.S. services and the eight other partner nations. While aircraft developments, such as the Russian PAK-FA or the Chinese J20, as argued by Airpower Australia, show that threats we could potentially face are becoming increasingly sophisticated, there is nothing new regarding development of these aircraft to change Defence's assessment." He then said that he thinks that the Air Power Australia's "analysis is basically flawed through incorrect assumptions and a lack of knowledge of the classified F-35 performance information."[180]

In a report released in 2013, it was stated that flaws in the fuel tank and fueldraulic (fuel-based hydraulic) systems have left it considerably more vulnerable to lightning strikes and other fire sources, including enemy fire than previously revealed, especially at lower altitudes.[181] This report updated a separate report from 2010, in which Lockheed Martin spokesman John Kent said that adding fire-suppression systems would offer "very small" improvement to survivability.[182] The same 2010 report also noted performance degradation of the three variants, the sustained turn rates had been reduced to 4.6 g for the F-35A, 4.5 g for the F-35B, and 5.0 g for the F-35C. The acceleration performance of all three variants was also downgraded, with the F-35C taking 43 seconds longer than an F-16 to accelerate from Mach 0.8 to Mach 1.2; this was judged by several fighter pilots to be a lower performance level than expected from a fourth generation fighter.[183] On 30 August 2013, it was reported that the F-35B and F-35C models take several complex maneuvers in order to "accelerate" to their top speed of Mach 1.6, which consumed almost all of the onboard fuel.[184] The F-35 program office is reconsidering addition of previously removed safety equipment.[185] In 2012, Lockheed Martin program manager Tom Burbage said that while the relatively large cross-sectional area of the fighter that was required by the internal weapons bays gave it a disadvantage against fourth generation fighters that were operating in a clear configuration. The F-35 armed with weapons carried internally had the advantage over fighters carrying their weapons outside the aircraft.[186]

In March 2013, USAF test pilots, flying with pre-operational software that did not utilize the all-aspect infrared AAQ-37 DAS sensor, noted a lack of visibility from the F-35 cockpit during evaluation flights, which would get them consistently shot down in combat. Defense spending analyst Winslow Wheeler concluded from flight evaluation reports that the F-35A "is flawed beyond redemption";[187] in response, program manager Bogdan suggested that pilots worried about being shot down should fly cargo aircraft instead.[188] The same report found (in addition to the usual problems with the aircraft listed above):

Current aircraft software is inadequate for even basic pilot training.

Ejection seat may fail, causing pilot fatality.

Several pilot-vehicle interface issues, including lack of feedback on touch screen controls.

The radar performs poorly, or not at all.

Engine replacement takes an average of 52 hours, instead of the two hours specified.

The JPO responded that more experienced pilots would be able to safely operate the aircraft and that procedures would improve over time.[190]

Even in the final "3F" software version, the F-35 will lack ROVER, in spite of having close air support as one of its primary missions.[191]

In 2014, David Axe stated design flaws related to its single-engine configuration could vex the F-35 for decades to come, forcing the Pentagon to suspend flying too often for the majority of its fighter fleet.[192]

In November 2014, China unveiled the portable JY-26 Skywatch-U UHF 3-D long-range surveillance radar system, specifically designed to defeat stealth aircraft like the F-35.[193] Responding to a reporters question about the High-Frequency radar threat General Welsh said "while we may have a new radar developed that allows an acquisition radar to see an airplane, that doesn't mean you can pass the track off to a radar that will then guide a weapon to be able to destroy the airplane. As long as we break the kill chain sometime between when you arrive in the battle space and when the enemy weapon approaches your airplane, you're successful at using stealth."[194]

A 2014 Pentagon report found these issues:

First two mission data sets available November 2015, after USMC IOC.

Overall suitability relies heavily on contractor support and unacceptable workarounds.

Aircraft availability reached 51% but short of 60% goal.

Fuel Tanks don't retain inerting for required 12 hours after landing.

High dynamic loads on the rudder at lower altitudes in 20-26 AoA preventing testing.

82 pounds added to F-35B in last 38 months, 337 pounds below limit.

Transonic Roll-Off (TRO) and airframe buffet continueto be a program concern.

In September 2012, the Pentagon criticized, quite publicly, Lockheed Martin's performance on the F-35 program and stated that it would not bail out the program again if problems with the plane's systems, particularly the helmet-mounted display, were not resolved. The deputy F-35 program manager said that the government's relationship with the company was the "worst I've ever seen" in many years of working on complex acquisition programs. Air Force Secretary Michael Donley told reporters the Pentagon had no more money to pour into the program after three costly restructurings in recent years. He said the department was done with major restructuring and that there was no further flexibility or tolerance for that approach. This criticism followed a "very painful" 7 September review that focused on an array of ongoing program challenges. Lockheed Martin responded with a brief statement saying it would continue to work with the F-35 program office to deliver the new fighter.[195]

On 28 September 2012, the Pentagon announced that the F-35 Joint Strike Fighter support program would become an open competition. They invited companies to participate in a two-day forum on 14–15 November for possible opportunities to compete for work managing the supply chain of the aircraft. Their reason is to reduce F-35 life-cycle costs by creating competition within the program and to refine its acquisition strategy and evaluate alternatives that will deliver the best value, long-term F-35 sustainment solution. This could be hazardous to Lockheed Martin, the current prime contractor for sustainment of all three variants, and selection of another company could reduce their revenues.[196]

In 2013, the officer in charge of the program blamed Lockheed Martin and Pratt & Whitney for gouging the government on costs, instead of focusing on the long term future of the program.[197]

In 2014, Lockheed was reported to be having problems with build quality, including one aircraft with a valve installed backwards and another with gaps in the stealth coating.[198]

Lockheed Martin's development roadmap extends until 2021, including a Block 6 engine improvement in 2019. The aircraft are expected to be upgraded throughout their operational lives.[199]

In September 2013, Northrop Grumman revealed the development of a company-funded Directional Infrared Counter Measures system in anticipation of a requirement to protect the F-35 from heat-seeking missiles. A laser jammer is expected to be part of the F-35 Block 5 upgrade; it must meet low-observability (LO) requirements and fit in the F-35's restricted space. Called the Threat Nullification Defensive Resource (ThNDR), it is to have a small, powerful laser, beam steering and LO window, use liquid cooling, and fit alongside the distributed aperture system (DAS) to provide spherical coverage with minimal changes; the DAS would provide missile warning and cue the jam head.[200]

Combat capabilities of the F-35 are made possible through software increments to advance technical abilities. Block 2A software enhanced simulated weapons, data link capabilities, and early fused sensor integration. Block 2B software enables the F-35 to provide basic close air support with certain JDAMs and the 500 lb GBU-12 Paveway II, as well as fire the AIM-120 AMRAAM. The Air Force is to declare the F-35 initially operational with Block 3i software. Full operational capability will come from Block 3F software; Block 3F enhances its ability to suppress enemy air defenses and enables the Lightning II to deploy the 500 lb JDAM, the GBU-53/B SDB II, and the AIM-9X Sidewinder. Block 4 software will increase the weapons envelope of the F-35 and is made to counter air defenses envisioned to be encountered past the 2040s. Block 4 upgrades will be broken into two increments; Block 4A in 2021 and Block 4B in 2023. This phase will also include usage of weaponry unique to British, Turkish, and other European countries who will operate Lightning II.[201]

Lockheed has offered the potential of "Higher Definition Video, longer range target detection and identification, Video Data Link, and Infrared (IR) Marker and Pointer" for the EOTS in future upgrades.[202]

F-35A prototype being towed to its inauguration ceremony on 7 July 2006

F-35B's thrust vectoring nozzle and lift fan

The F-35 appears to be a smaller, single-engine sibling of the twin-engine Lockheed Martin F-22 Raptor, and indeed drew elements from it. The exhaust duct design was inspired by the General Dynamics Model 200 design, proposed for a 1972 supersonic VTOL fighter requirement for the Sea Control Ship.[203] Lockheed consulted with the Yakovlev Design Bureau in the F-35B STOVL variant's development, purchasing design data from their development of the Yakovlev Yak-141 "Freestyle".[204] Although several experimental designs have been developed since the 1960s, such as the unsuccessful Rockwell XFV-12, the F-35B is to be the first operational supersonic, STOVL stealth fighter.[205]

Acquisition deputy to the assistant secretary of the Air Force, Lt. Gen. Mark D. "Shack" Shackelford has said that the F-35 is designed to be America's "premier surface-to-air missile killer and is uniquely equipped for this mission with cutting edge processing power, synthetic aperture radar integration techniques, and advanced target recognition."[206][207] Lockheed Martin states the F-35 is intended to have close- and long-range air-to-air capability second only to that of the F-22 Raptor.[208] Lockheed Martin has said that the F-35 has the advantage over the F-22 in basing flexibility and "advanced sensors and information fusion".[209] Lockheed Martin has suggested that the F-35 could replace the USAF's F-15C/D fighters in the air superiority role and the F-15E Strike Eagle in the ground attack role.[210]

Integrated avionics and sensor fusion that combine information from off- and on-board sensors to increase the pilot's situational awareness and improve target identification and weapon delivery, and to relay information quickly to other command and control (C2) nodes;

The Autonomic Logistics Global Sustainment (ALGS), Autonomic Logistics Information System (ALIS) and Computerized maintenance management system (CMMS) are to help ensure aircraft uptime with minimal maintenance manpower.[215] The Pentagon has moved to open up the competitive bidding by other companies.[216] This was after Lockheed Martin stated that instead of costing twenty percent less than the F-16 per flight hour, the F-35 would actually cost twelve percent more.[217] Though the ALGS is intended to reduce maintenance costs, the company disagrees with including the cost of this system in the aircraft ownership calculations.[218] The USMC have implemented a workaround for a cyber vulnerability in the system.[219]

Electro-hydrostatic actuators run by a power-by-wire flight-control system.[220]

A modern and updated flight simulator, which may be used for a greater fraction of pilot training in order to reduce the costly flight hours of the actual aircraft.[221]

Lightweight, powerful and volatile Lithium-ion batteries similar to those that have grounded the Boeing 787 Dreamliner fleet.[222] These are required to provide power to run the control surfaces in an emergency,[223] and have been strenuously tested.[224]

Structural composites in the F-35 are 35% of the airframe weight (up from 25% in the F-22).[225] The majority of these are bismaleimide (BMI) and composite epoxy material.[226] The F-35 will be the first mass produced aircraft to include structural nanocomposites, namely carbon nanotube reinforced epoxy.[227] Experience of the F-22's problems with corrosion lead to the F-35 using a gap filler that causes less galvanic corrosion to the airframe's skin, designed with fewer gaps requiring filler and implementing better drainage.[228] The relatively short 35-foot wingspan of the A and B variants is set by the F-35B's requirement to fit inside the Navy's current amphibious assault ship parking area[229] and elevators; the F-35C's longer wing is considered to be more fuel efficient.[230]

A United States Navy study found that the F-35 will cost 30 to 40 percent more to maintain than current jet fighters;[231] not accounting for inflation over the F-35's operational lifetime. A Pentagon study concluded a $1 trillion maintenance cost for the entire fleet over its lifespan, not accounting for inflation.[232] The F-35 program office found that as of January 2014, costs for the F-35 fleet over a 53-year life cycle was $857 billion. Costs for the fighter have been dropping and accounted for the 22 percent life cycle drop since 2010.[233] Lockheed claims that by 2019, pricing for the fifth-generation aircraft will be less than fourth-generation fighters. An F-35A in 2019 is expected to cost $85 million per unit complete with engines and full mission systems, inflation adjusted from $75 million in December 2013.[234]

The Pratt & Whitney F135 powers the F-35. An alternative engine, the General Electric/Rolls-Royce F136, was being developed until it was cancelled by its manufacturers in December 2011.[235][236] Neither the F135 or F136 engines are designed to supercruise,[237] the F-35 can achieve a limited supercruise of Mach 1.2 for 150 miles.[238] The F135 is the second (radar) stealthy afterburning jet engine. Like the Pratt & Whitney F119 it was derived from, the F135 has suffered afterburner pressure pulsations, or 'screech' at low altitude and high speed.[239] The F-35 has a maximum speed of over Mach 1.6. With a maximum takeoff weight of 60,000 lb (27,000 kg),[N 2][241] the Lightning II is considerably heavier than the lightweight fighters it replaces.

The STOVL F-35B is outfitted with the Rolls-Royce LiftSystem, designed by Lockheed Martin and developed by Rolls-Royce. This system more resembles the Russian Yak-141 and German VJ 101D/E than the preceding STOVL Harrier Jump Jet and the Rolls-Royce Pegasus engine.[242][243][244] The Lift System is composed of a lift fan, drive shaft, two roll posts and a "Three Bearing Swivel Module" (3BSM).[245] The 3BSM is a thrust vectoringnozzle which allows the main engine exhaust to be deflected downward at the tail of the aircraft. The lift fan is near the front of the aircraft and provides a counterbalancing thrust using two counter-rotating blisks.[246] It is powered by the engine's low-pressure (LP) turbine via a drive shaft and gearbox. Roll control during slow flight is achieved by diverting unheated engine bypass air through wing-mounted thrust nozzles called Roll Posts.[247][248]

F136 funding came at the expense of other program elements, impacting on unit costs.[249] The F136 team claimed their engine had a greater temperature margin, potentially critical for VTOL operations in hot, high altitude conditions.[250] Pratt & Whitney tested higher thrust versions of the F135, partly in response to GE's claims that the F136 is capable of producing more thrust than the 43,000 lbf (190 kN) of early F135s. In testing, the F135 has demonstrated a maximum thrust of over 50,000 lbf (220 kN);[251] making it the most powerful engine ever installed in a fighter aircraft as of 2010.[252] It is much heavier than previous fighter engines; the Heavy Underway Replenishment system needed to transfer the F135 between ships is an unfunded USN requirement.[253]Thermoelectric-powered sensors monitor turbine bearing health.[254]

Lockheed Martin states that the weapons load can be configured as all-air-to-ground or all-air-to-air, and has suggested that a Block 5 version will carry three weapons per bay instead of two, replacing the heavy bomb with two smaller weapons such as AIM-120 AMRAAM air-to-air missiles.[265] Upgrades are to allow each weapons bay to carry four GBU-39 Small Diameter Bombs (SDB) for A and C models, or three in F-35B.[266] Another option is four GBU-53/B Small Diameter Bomb IIs in each bay on all F-35 variants.[267] One F-35 has been outfitted with four SDB II bombs and an AMRAAM missile to test adequate bay door clearance.[268] The Meteor (missile) air-to-air missile may be adapted for the F-35, a modified Meteor with smaller tailfins for the F-35 was revealed in September 2010; plans call for the carriage of four Meteors internally.[269] The United Kingdom planned to use up to four AIM-132 ASRAAM missiles internally, later plans call for the carriage of two internal and two external ASRAAMs.[270] The external ASRAAMs are planned to be carried on "stealthy" pylons; the missile allows attacks to slightly beyond visual range without employing radar.[255][271]

Norway and Australia are funding an adaptation of the Naval Strike Missile (NSM) for the F-35. Under the designation Joint Strike Missile (JSM), it is to be the only cruise missile to fit the F-35's internal bays; according to studies two JSMs can be carried internally with an additional four externally.[272] The F-35 is expected to take on the Wild Weasel mission, though there are no planned anti-radiation missiles for internal carriage.[273] The B61 nuclear bomb was initially scheduled for deployment in 2017;[274] as of 2012 it was expected to be in the early 2020s,[275] and in 2014 Congress moved to cut funding for the needed weapons integration work.[276]Norton A. Schwartz agreed with the move and said that "F-35 investment dollars should realign to the long range strike bomber".[277] NATO partners who are buying the F-35 but cannot afford to make them dual-capable want the USAF to fund the conversions to allow their Lightning IIs to carry thermonuclear weapons. The USAF is trying to convince NATO partners who can afford the conversions to contribute to funding for those that cannot. The F-35 Block 4B will be able to carry two B61 nuclear bombs internally by 2024.[278]

The Air Force plans to use the F-35A to primarily take up the close air support (CAS) mission in contested environments. Amid criticism that the aircraft is not well suited for the role compared to a dedicated attack platform, Air Force chief of staff Mark Welsh is putting focus on weapons for the F-35 to employ on CAS sorties including guided rockets, fragmentation rockets that would shatter into individual projectiles before impact, and lighter, smaller ammunition in higher capacity gun pods.[283]

The Fighter Teen Series (F-15, F-16, F/A-18) carried large external fuel tanks, but to avoid negating its stealth characteristics the F-35 must fly most missions without them. Unlike the F-16 and F/A-18, the F-35 lacks leading edge extensions and instead uses stealth-friendly chines for vortex lift in the same fashion as the SR-71 Blackbird.[263] The small bumps just forward of the engine air intakes form part of the diverterless supersonic inlet (DSI) which is a simpler, lighter means to ensure high-quality airflow to the engine over a wide range of conditions. These inlets also crucially improve the aircraft's very-low-observable characteristics (by eliminating radar reflections between the diverter and the aircraft's skin).[287] Additionally, the "bump" surface reduces the engine's exposure to radar, significantly reducing a strong source of radar reflection[288] because they provide an additional shielding of engine fans against radar waves. The Y-duct type air intake ramps also help in reducing RCS, because the intakes run parallel and not directly into the engine fans.

F-35A front profile in flight. The doors are opened to expose the aerial refueling inlet valve.

In June 2014, General Mike Hostage, Commander of the Air Combat Command, stated that the F-35 was stealthier than the F-22.[289] Independent critic Carlo Kopp disagrees, asserting that the F-22 was designed to be difficult to detect by all types of radars and from all directions.[290] Kopp claims that the F-35 manifests its lowest radar cross-section from the frontal aspect due to what he calls design compromises; that its surfaces are only shaped to best defeat radars operating in the X band and upper S band, typically found on fighters, surface-to-air missiles and their tracking radars, and that the F-35 would be easier to detect using other radar frequencies.[290] Because the aircraft's shape is important to the radar cross-section (RCS), special care must be taken to match the "boilerplate" during production.[291] Ground crews require Repair Verification Radar (RVR) test sets to verify the RCS after performing repairs, which is not a concern for non-stealth aircraft.[292][293]

In 2008, the Air Force revealed that the F-35 would be about twice as loud at takeoff as the McDonnell Douglas F-15 Eagle and up to four times as loud during landing.[294] Residents near Luke Air Force Base, Arizona and Eglin Air Force Base, Florida, possible F-35 bases, requested environmental impact studies be conducted regarding the F-35's noise levels.[294] In 2009, the city of Valparaiso, Florida, adjacent to Eglin AFB, threatened to sue over the impending F-35 arrival; this lawsuit was settled in March 2010.[295][296][297] In 2009, testing reportedly revealed the F-35 to be: "only about as noisy as an F-16 fitted with a Pratt & Whitney F100-PW-200 engine...quieter than the Lockheed Martin F-22 Raptor and the Boeing F/A-18E/F Super Hornet."[298] An acoustics study by Lockheed Martin and the Air Force found F-35's noise levels to be comparable to the F-22 and F/A-18E/F.[299] A USAF environmental impact study found that replacing F-16s with F-35s at Tucson International Airport would subject more than 21 times as many residents to extreme noise levels.[300] The USN will need to redesign hearing protection for sailors to protect against the "thundering 152 decibels" of the F-35.[301] The Joint Strike Fighter program office found in October 2014 that the F-35B's take-off noise was only two decibels higher than a Super Hornet, a virtually indistinguishable difference to the human ear, and is even 10 decibels quieter when flying formations or landing.[302]

A helmet-mounted display system (HMDS) will be fitted to all models of the F-35.[306] While some fighters have offered HMDS along with a head up display (HUD), this will be the first time in several decades that a front line fighter has been designed without a HUD.[307] The F-35 is equipped with a right-hand HOTASside stick controller. The Martin-Baker US16E ejection seat is used in all F-35 variants.[308] The US16E seat design balances major performance requirements, including safe-terrain-clearance limits, pilot-load limits, and pilot size; it uses a twin-catapult system housed in side rails.[309] The F-35 employs an oxygen system derived from the F-22's own system, which has been involved in multiple hypoxia incidents on that aircraft; unlike the F-22, the flight profile of the F-35 is similar to other fighters that routinely use such systems.[310][311]

Six additional passive infrared sensors are distributed over the aircraft as part of Northrop Grumman's electro-optical AN/AAQ-37 Distributed Aperture System (DAS),[28] which acts as a missile warning system, reports missile launch locations, detects and tracks approaching aircraft spherically around the F-35, and replaces traditional night vision devices. All DAS functions are performed simultaneously, in every direction, at all times. The Electronic warfare systems are designed by BAE Systems and include Northrop Grumman components.[319] Functions such as the Electro-Optical Targeting System and the Electronic Warfare system are not usually integrated on fighters.[320] The F-35's DAS is so sensitive, it reportedly detected the launch of an air-to-air missile in a training exercise from 1,200 mi (1,900 km) away, which in combat would give away the location of an enemy aircraft even if it had a very low radar cross-section.[321]

The communications, navigation and identification (CNI) suite is designed by Northrop Grumman and includes the Multifunction Advanced Data Link (MADL), as one of a half dozen different physical links.[322] The F-35 will be the first fighter with sensor fusion that combines radio frequency and IR tracking for continuous all-direction target detection and identification which is shared via MADL to other platforms without compromising low observability.[240] The non-encrypted Link 16 is also included for communication with legacy systems.[323] The F-35 has been designed with synergy between sensors as a specific requirement, the aircraft's "senses" being expected to provide a more cohesive picture of the battlespace around it and be available for use in any possible way and combination with one another; for example, the AN/APG-81 multi-mode radar also acts as a part of the electronic warfare system.[324] The Program Executive Officer (PEO) General Bogdan has described the sensor fusion software as one of the most difficult parts of the program.[325]

Much of the F-35's software is written in C and C++ due to programmer availability, Ada83 code also is reused from the F-22.[326] The Integrity DO-178B real-time operating system (RTOS) from Green Hills Software runs on COTS Freescale PowerPC processors.[327] The final Block 3 software is planned to have 8.6 million lines of code.[328] In 2010, Pentagon officials discovered that additional software may be needed.[329] General Norton Schwartz has said that the software is the biggest factor that might delay the USAF's initial operational capability.[330] In 2011, Michael Gilmore, Director of Operational Test & Evaluation, wrote that, "the F-35 mission systems software development and test is tending towards familiar historical patterns of extended development, discovery in flight test, and deferrals to later increments."[331]

The electronic warfare and electro-optical systems are intended to detect and scan aircraft, allowing engagement or evasion of a hostile aircraft prior to being detected.[324] The CATbird avionics testbed has proved capable of detecting and jamming radars, including the F-22's AN/APG-77.[332] The F-35 was previously considered a platform for the Next Generation Jammer; attention shifted to using unmanned aircraft in this capacity instead.[333] Several subsystems use Xilinx FPGAs;[334] these COTS components enable supply refreshes from the commercial sector and fleet software upgrades for the software-defined radio systems.[327]

Lockheed Martin's Dave Scott claims that sensor fusion boosts engine thrust and oil efficiency, increasing the aircraft's range.[335] Air Force official Ellen M. Pawlikowski has proposed using the F-35 to control and coordinate multiple unmanned combat aerial vehicles (UCAVs). Using its sensors and communications equipment, a single F-35 could orchestrate an attack made by up to 20 armed UCAVs.[336]

The F-35 does not need to be physically pointing at its target for weapons to be successful.[257][337] Sensors can track and target a nearby aircraft from any orientation, provide the information to the pilot through their helmet (and therefore visible no matter which way the pilot is looking), and provide the seeker-head of a missile with sufficient information. Recent missile types provide a much greater ability to pursue a target regardless of the launch orientation, called "High Off-Boresight" capability. Sensors use combined radio frequency and infra red (SAIRST) to continually track nearby aircraft while the pilot's helmet-mounted display system (HMDS) displays and selects targets; the helmet system replaces the display-suite-mounted head-up display used in earlier fighters.[338]

The F-35's systems provide the edge in the "observe, orient, decide, and act" OODA loop; stealth and advanced sensors aid in observation (while being difficult to observe), automated target tracking helps in orientation, sensor fusion simplifies decision making, and the aircraft's controls allow the pilot to keep their focus on the targets, rather than the controls of their aircraft.[339][N 3]

Problems with the Vision Systems International helmet-mounted display led Lockheed Martin-Elbit Systems to issue a draft specification for alternative proposals in early 2011, to be based around the Anvis-9 night vision goggles.[340] BAE Systems was selected to provide the alternative system in late 2011.[341] The BAE Systems alternative helmet was to include all the features of the VSI system.[342] Adopting the alternative helmet would have required a cockpit redesign,[343] but in 2013 development on the alternative helmet was halted due to progress on the baseline helmet.[344] The third generation helmet will begin flight tests in 2014.[345]

In 2011, Lockheed Martin-Elbit granted VSI a contract to fix the vibration, jitter, night-vision and sensor display problems in their helmet-mounted display.[346] A speculated potential improvement is the replacement of Intevac’s ISIE-10 day/night camera with the newer ISIE-11 model.[347] In October 2012, Lockheed Martin-Elbit stated that progress had been made in resolving the technical issues of the helmet-mounted display, and cited positive reports from night flying tests; it had been questioned whether the helmet system allows pilots enough visibility at night to carry out precision tasks.[348] In 2013, in spite of continuing problems with the helmet display, the F-35B model completed 19 nighttime vertical landings onboard the USS Wasp at sea,[349] by using the DAS instead of the helmet's built-in night vision capabilities, which offer at best 20/35 vision.[350]

In October 2013, development of the alternate helmet was halted. The current Gen 2 helmet is expected to meet the requirements to declare, in July 2015, that the F-35 has obtained initial operational capability. Beginning in 2016 with low rate initial production (LRIP) lot 7, the program will introduce a Gen 3 helmet that features an improved night vision camera, new liquid crystal displays, automated alignment and other software enhancements.[344]

The program's maintenance concept is for any F-35 to be maintained in any F-35 maintenance facility and that all F-35 parts in all bases will be globally tracked and shared as needed.[351] The commonality between the different variants has allowed the USMC to create their first aircraft maintenance Field Training Detachment to directly apply the lessons of the USAF to their F-35 maintenance operations.[352] The aircraft has been designed for ease of maintenance, with 95% of all field replaceable parts "one deep" where nothing else has to be removed to get to the part in question. For instance the ejection seat can be replaced without removing the canopy, the use of low-maintenance electro-hydrostatic actuators instead of hydraulic systems and an all-composite skin without the fragile coatings found on earlier stealth aircraft.[353]

The F-35 has received good reviews from pilots and maintainers, suggesting it is performing better than its predecessors did at a similar stage of development. The stealth type has proved relatively stable from a maintenance standpoint. Part of the improvement is attributed to better maintenance training, as F-35 maintainers have received far more extensive instruction at this early stage of the program than on the F-22 Raptor. The F-35's stealth coatings are much easier to work with than those used on the Raptor. Cure times for coating repairs are lower and many of the fasteners and access panels are not coated, further reducing the workload for maintenance crews. Some of the F-35's radar-absorbent materials are baked into the jet's composite skin, which means its stealthy signature is not easily degraded.[354] It is still harder to maintain (due to its stealth) than fourth-generation aircraft.[355]

The first F-35A (designated AA-1) was rolled out in Fort Worth, Texas, on 19 February 2006. In September 2006, the first engine run of the F135 in an airframe took place.[356] On 15 December 2006, the F-35A completed its maiden flight.[357] A modified Boeing 737–300, the Lockheed CATBird has been used as an avionics test-bed for the F-35 program, including a duplication of the cockpit.[265]

The first F-35B (designated BF-1) made its maiden flight on 11 June 2008, piloted by BAE Systems' test pilot Graham Tomlinson. Flight testing of the STOVL propulsion system began on 7 January 2010.[358] The F-35B's first hover was on 17 March 2010, followed by its first vertical landing the next day.[359] During a test flight on 10 June 2010, the F-35B STOVL aircraft achieved supersonic speeds[360] as had the X-35B before.[361] In January 2011, Lockheed Martin reported that a solution had been found for the cracking of an aluminum bulkhead during ground testing of the F-35B.[362] In 2013, the F-35B suffered another bulkhead cracking incident.[363] This will require redesign of the aircraft, which is already very close to the ultimate weight limit.[364]

The first delivered USAF F-35 on its delivery flight to Eglin Air Force Base in July 2011.

By June 2009, many of the initial flight test targets had been accomplished but the program was behind schedule.[365] During 2008, a Pentagon Joint Estimate Team (JET) estimated that the program was two years behind the public schedule, a revised estimate in 2009 predicted a 30-month delay.[366] Delays reduced planned production numbers by 122 aircraft through 2015 to provide an addition 2.8 billion for development; internal memos suggested that the official timeline would be extended by 13 months.[366][367] The success of the JET led Ashton Carter calling for more such teams for other poorly performing projects.[368]

Nearly 30 percent of test flights required more than routine maintenance to make the aircraft flightworthy again.[369] As of March 2010, the F-35 program had used a million more man-hours than predicted.[370] The United States Navy projected that lifecycle costs over a 65-year fleet life for all American F-35s to be $442 billion higher than U.S. Air Force projections.[371] F-35 delays have led to shortfall of up to 100 jet fighters in the Navy/Marines team, although measures have been taken using existing assets to manage and reduce this shortfall.[372]

The F-35C's maiden flight took place on 7 June 2010, at NAS Fort Worth JRB. A total of 11 U.S. Air Force F-35s arrived in fiscal year 2011.[373] On 9 March 2011, all F-35s were grounded after a dual generator failure and oil leak in flight;[374] the cause of the incident was discovered to have been the result of faulty maintenance.[375] In 2012, Navy Commander Erik Etz of the F-35 program office commented that rigorous testing of the F-35's sensors had taken place during exercise Northern Edge 2011, and had served as a significant risk-reduction step.[376][377]

On 2 August 2011, an F-35's integrated power package (IPP) failure during a standard engine test at Edwards Air Force Base led to the F-35 being immediately grounded for two weeks.[378][379] On 10 August 2011, ground operations were re-instituted; preliminary inquiries indicated that a control valve did not function properly, leading to the IPP failure.[380][381] On 18 August 2011, the flight ban was lifted for 18 of the 20 F-35s; two aircraft remained grounded due to a lack of monitoring systems.[382] The IPP suffered a second software-related incident in 2013, this resulted in no disruption as the fleet was already grounded due to separate engine issues.[383]

On 25 October 2011, the F-35A reached its designed top speed of Mach 1.6 for the first time.[384] Further testing demonstrated Mach 1.61 and 9.9g.[385] On 11 February 2013, an F-35A completed its final test mission for clean wing flutter, reporting to be clear of flutter at speeds up to Mach 1.6.[386] On 15 August 2012, an F-35B completed airborne engine start tests.[387]

During testing in 2011, all eight landing tests of the F-35C failed to catch the arresting wire; a redesigned tail hook was developed and delivered two years later in response.[388][389] In October 2011, two F-35Bs conducted three weeks of initial sea trials aboard USS Wasp.[390]

On 6 October 2012, the F-35A dropped its first bomb,[391] followed three days later by an AIM-120 AMRAAM.[392] On 28 November 2012, an F-35C performed a total of eleven weapon releases, ejecting a GBU-31 JDAM and GBU-12 Paveway from its weapons bay in the first ground weapons ejections for the F-35C.[393] On 5 June 2013, an F-35A at the Point Mugu Sea Test Range completed the first in-flight missile launch of an AIM-120 C5 AAVI (AMRAAM Air Vehicle Instrumented). It was launched from the internal weapons bay.[394]

On 16 November 2012, the U.S. Marines received the first F-35B at MCAS Yuma, and the VMFA(AW)-121 unit is to be redesignated from a Boeing F/A-18 Hornet unit to an F-35B squadron.[395] A February 2013 Time article revealed that Marine pilots are not allowed to perform a vertical landing—the maneuver is deemed too dangerous, and it is reserved only for Lockheed test pilots.[396] On 10 May 2013, the F-35B completed its first vertical takeoff test.[397] On 3 August 2013, the 500th vertical landing of an F-35 took place.[398]

On 18 January 2013, the F-35B was grounded after the failure of a fueldraulic line in the propulsion system on 16 January.[399] The problem was traced to an "improperly crimped" fluid line manufactured by Stratoflex.[400][401] The Pentagon cleared all 25 F-35B aircraft to resume flight tests on 12 February 2013.[402] On 22 February 2013, the U.S. Department of Defense grounded the entire fleet of 51 F-35s after the discovery of a cracked turbine blade in a U.S. Air Force F-35A at Edwards Air Force Base.[403] On 28 February 2013, the grounding was lifted after an investigation concluded that the cracks in that particular engine resulted from stressful testing, including excessive heat for a prolonged period during flight, and did not reflect a fleetwide problem.[404][405] The F-35C Lightning II carrier variant Joint Strike Fighter conducted its first carrier-based night flight operations aboard an aircraft carrier off the coast of San Diego on 13 November 2014.[406]

In 2011, the Director of Operational Test and Evaluation warned that the USAF's plan to start unmonitored flight training "risks the occurrence of a serious mishap".[407] The leaders of the United States Senate Committee on Armed Services called on Defense Secretary Leon Panetta to address the issue.[408] Despite the objections, expanded trial flights began in September 2012.[409]

(From the top) 33rd FW F-35A, F-35B and F-35C near Eglin AFB in May 2014.

The F-35A and F-35B were cleared for flight training in early 2012.[410] A military flight release for the F-35A was issued on 28 February 2012.[411] The aircraft were restricted to basic maneuvers with no tactical training allowed.[412] On 24 August 2012, an F-35 flew its 200th sortie while at Eglin Air Force Base, flown by a Marine pilot. The pilot said, "The aircraft have matured dramatically since the early days. The aircraft are predictable and seem to be maintainable, which is good for the sortie production rate. Currently, the flight envelope for the F-35 is very, very restricted, but there are signs of improvement there too." The F-35s at the base no longer need to fly with a chase aircraft and are operating in a normal two-ship element.[413]

On 21 August 2012, J. Michael Gilmore wrote that he would not approve the Operational Test and Evaluation master plan until his concerns about electronic warfare testing, budget and concurrency were addressed.[414] On 7 September 2012, the Pentagon failed to approve a comprehensive operational testing plan for the F-35.[415] Instead, on 10 September 2012, the USAF began an operational utility evaluation (OUE) of the F-35A entire system, including logistical support and maintenance, maintenance training, pilot training, and pilot execution.[416] By 1 October, the OUE was reported as "proceeding smoothly", pilots started on simulators prior to flying on 26 October.[417] The OUE was completed on 14 November with the 24th flight, the four pilots involved having completed six flights each.[418]

During the Low Rate Initial Production (LRIP) phase of the aircraft, the U.S. had taken a tri-service approach to developing tactics and procedures for the F-35 using flight simulators prior to the type entering service. Simulated flights had tested the flight controls' effectiveness, helping to discover technical problems and refine aircraft design.[419] Maintenance personnel have discovered that it is possible to correct deficiencies in the F-35, which is a software-defined aircraft, simply by rebooting the aircraft's software and onboard systems.[420]

Air Force pilot training F-35A began in January 2013 at Eglin Air Force Base; the program currently has a maximum capacity of 100 military pilots and 2,100 maintainer students.[421]

On 23 June 2014, an F-35A experienced a fire in the engine area during its takeoff at Eglin AFB. In response, the Pentagon's Joint Program Office halted training in all F-35 models the next day,[422][423] and on 3 July, the F-35 fleet was formally grounded.[424] The fleet was returned to flight on 15 July,[425] but the engine inspection regimen caused the aircraft's debut at the Farnborough 2014 Air Show to be canceled.[426][427]

On 9 December 2010, a media report stated that the "USMC will base 216 F-35Bs on the East Coast and 184 of them on the West Coast, documents showed." This report continued to state that, "Cherry Point will get 128 jets to form eight squadrons; Beaufort will have three squadrons and a pilot training center using 88 aircraft; Miramar will form six operational squadrons with 96 jets and 88 F-35s will go to Yuma for five operational squadrons with an additional test and evaluation unit."[428]

In 2011, the USMC and USN signed an agreement that the USMC will purchase 340 F-35B and 80 F-35C fighters. The five squadrons of USMC F-35Cs would be assigned to Navy carriers while F-35Bs would be used ashore.[429][430]

On 11 March 2014, the first F-35A Lightning II assigned to Luke Air Force Base arrived at the base. A total of 16 F-35s are to be delivered to the base by the end of 2014, with 144 Lightning IIs to be stationed there arriving over the course of the next decade.[431][432]

On 8 January 2015, the Royal Air Force base, RAF Lakenheath in the UK, was chosen as the first U.S. Air Force European base to station two F-35 squadrons, following an announcement by the Pentagon. A total of 48 F-35s, making up two squadrons, will add to the 48th Fighter Wing's already existing F-15C and F-15E Strike Eagle jets.[433]

While the United States is the primary customer and financial backer, the United Kingdom, Italy, the Netherlands, Canada, Turkey, Australia, Norway, and Denmark have agreed to contribute US$4.375 billion towards development costs.[434] Total development costs are estimated at more than US$40 billion. The purchase of an estimated 2,400 aircraft is expected to cost an additional US$200 billion.[435] The initial plan was that the nine major partner nations would acquire over 3,100 F-35s through 2035.[436] Sales to partner nations are made through the Pentagon's Foreign Military Sales program.[437]

There are three levels of international participation.[438] The levels generally reflect financial stake in the program, the amount of technology transfer and subcontracts open for bid by national companies, and the order in which countries can obtain production aircraft. The United Kingdom is the sole "Level 1" partner, contributing US$2.5 billion, which was about 10% of the planned development costs[439] under the 1995 Memorandum of Understanding that brought the UK into the project.[440] Level 2 partners are Italy, which is contributing US$1 billion; and the Netherlands, US$800 million. Level 3 partners are Turkey, US$195 million; Canada, US$160 million; Australia, US$144 million; Norway, US$122 million and Denmark, US$110 million. Israel and Singapore have joined as Security Cooperative Participants (SCP).[441][442][443] Japan announced on 20 December 2011 its intent to purchase 42 F-35s with deliveries beginning in 2016 to replace the F-4 Phantom II; Japan seeks 38 F-35s, to be assembled domestically.[444]

By 2012, many changes had occurred in the order book. Italy became the first country to announce a reduction of its overall fleet procurement, cutting its buy from 131 to 90 aircraft. Other nations reduced initial purchases or delayed orders while still intending to purchase the same final numbers. The United States canceled the initial purchase of 13 F-35s and postponed orders for another 179. The United Kingdom cut its initial order and delayed a decision on future orders. Australia decided to buy the Boeing F/A-18E/F Super Hornet as an interim measure. Turkey also cut its initial order of four aircraft to two, but confirmed plans to purchase 100 F-35As.[445][446] Turkey will buy four F-35s to be delivered in 2015 and 2016, while the order may be increased from 100 to 120 aircraft.[447] These changes resulted in increased procurement prices, and increased the likelihood of further cuts.[448][449]

On 3 April 2012, the Auditor General of CanadaMichael Ferguson published a report outlining problems with Canada's procurement of the jet, including misinformation over the final cost. According to the Auditor General, the government knowingly understated the final price of the 65 jets by $10 billion.[450] Canada's Conservative government had stated it would not reduce its order, claiming an anticipated $75–80 million unit cost; the procurement was termed a "scandal" and "fiasco" by the media and faced a full review to determine any Canadian F-35 purchase.[451][452][453] On 13 December 2012, in a scathing editorial published by CBC News, journalist Brian Stewart termed the F-35 project a "global wrecking ball" due to its run-away costs and lack of affordability for many participating nations.[454]

In May 2013, Lockheed Martin declared that Turkey is projected to earn $12 billion from licensed production of F-35 components.[455][456]

In November 2014, the United Kingdom confirmed its first order for 14 F-35Bs to be delivered in 2016.[457]

The F-35A is the conventional takeoff and landing (CTOL) variant intended for the U.S. Air Force and other air forces. It is the smallest, lightest F-35 version and is the only variant equipped with an internal cannon, the GAU-22/A. This 25 mm cannon is a development of the GAU-12 carried by the USMC's AV-8B Harrier II. It is designed for increased effectiveness against ground targets compared to the 20 mmM61 Vulcan cannon carried by other USAF fighters.

The F-35A is expected to match the F-16 in maneuverability and instantaneous and sustained high-g performance, and outperform it in stealth, payload, range on internal fuel, avionics, operational effectiveness, supportability, and survivability.[466] It is expected to match an F-16 that is carrying the usual external fuel tank in acceleration performance.[467]

The A variant is primarily intended to replace the USAF's F-16 Fighting Falcon. At one point it was also intended to replace the A-10 Thunderbolt II starting in 2028.[468][469] The F-35A can be outfitted to receive fuel via either of the two main aerial refueling methods; this was a consideration in the Canadian procurement and a deciding factor for the Japanese purchase.[470][471][472] On 18 December 2013, the Netherlands became the second partner country to operate the F-35A, when Maj. Laurens J.W. Vijge of the Royal Netherlands Air Force took off from Eglin Air Force Base.[473]

On 27 January 2014, General Mike Hostage, head of Air Combat Command, stated he would fight "to the death" to not have a single plane of the USAF's 1,763 plane planned F-35 purchase be cut, because the allies and partners of the US got "weak in the knees" when seeing the USAF "back away" from the F-35. He said the F-15 and F-16 fleets would become tactically obsolete in the middle of the next decade regardless of improvements. Hostage also commented that the F-35 would be "irrelevant" without the F-22 fleet being viable as the F-35 was not an air superiority fighter.[474]

An F-35B lands aboard the amphibious assault ship USS Wasp, in August 2013.

F-35B short-takeoff from USS Wasp during its first sea trials, October 2011.

The F-35B is the short takeoff and vertical landing (STOVL) variant of the aircraft. Similar in size to the A variant, the B sacrifices about a third of the other version's fuel volume to accommodate the vertical flight system. Vertical takeoffs and landings are riskier due to threats such as foreign object damage.[475][476] Whereas the F-35A is stressed to 9 g,[477][478] the F-35B's stress goal is 7 g. As of 2014[update], the F-35B is limited to 4.5 g and 400 knots. Next software upgrade includes weapons, 5.5 g and Mach 1.2, with a final target of 7 g and Mach 1.6.[479] The first test flight of the F-35B was conducted on 11 June 2008.[480]

Unlike other variants, the F-35B has no landing hook. The "STOVL/HOOK" control instead engages conversion between normal and vertical flight.[481] Jet thrust is sent directly downwards during vertical flight; the nozzle is being redesigned to spread the output across an oval rather than circular shape in order to limit damage to asphalt and ship decks.[482] The variant's three-bearing swivel nozzle that directs the full thrust of the engine is moved by a “fueldraulic” actuator using pressurized fuel.[483]

The United States Marine Corps plans to purchase 340 F-35Bs,[79] to replace current inventories of both the F/A-18 Hornet (A, B, C and D-models), and the AV-8B Harrier II, in the fighter and attack roles.[484] The Marines plan to use the F-35B from "unimproved surfaces at austere bases" but with "special, high-temperature concrete designed to handle the heat."[485][486] The USMC intends to declare Initial Operational Capability with about 50 F-35s running interim Block 2B software in the 2014 to 2015 timeframe.[487] The USAF had considered replacing the A-10 with the F-35B, but will not do so due to the F-35B's inability to generate enough sorties.[488]

On 6 January 2011, Gates said that the 2012 budget would call for a two-year pause in F-35B production during which the aircraft faced redesign, or cancellation if unsuccessful.[74][489] In 2011, Lockheed Martin executive vice president Tom Burbage and former Pentagon director of operational testing Tom Christie stated that most program delays were due to the F-35B, which forced massive redesigns of other versions.[490] Lockheed Martin Vice President Steve O’Bryan has said that most F-35B landings will be conventional to reduce stress on vertical lift components.[491] These conventional mode takeoffs and landings cause "an unacceptable wear rate" to the aircraft's poorly designed tires.[492] USMC Lt. Gen. Robert Schmidle has said that the vertical lift components would only be used "a small percentage of the time" to transfer the aircraft from carriers to land bases.[493] On 3 October 2011, the F-35B began its initial sea-trials by performing a vertical landing on the deck of the amphibious assault ship USS Wasp.[494] Probation status was reportedly ended by Defense Secretary Leon Panetta in January 2012 due to progress made.[77]

In 2011, the Italian Navy was preparing Grottaglie Air Station for F-35B operations; they are to receive 22 aircraft between 2014 and 2021, with the aircraft carrier Cavour set to be modified to operate them by 2016.[503] Commandant of the U.S. Marine Corps, General James Amos has said that, in spite of increasing costs and schedule delays, there is no plan B to the F-35B.[504] The F-35B is larger than the aircraft it replaces, which required USS America to be designed without well deck capabilities.[505] In 2011, the USMC and USN signed an agreement that the USMC will purchase 340 F-35B and 80 F-35C fighters while the USN will purchase 260 F-35C fighters. The five squadrons of USMC F-35Cs will be assigned to Navy carriers while F-35Bs will be used on amphibious ships and ashore.[429][430]

Although the Australian Canberra-classlanding helicopter dock ships were not originally planned to operate fixed-wing aircraft, in May 2014, the Minister for DefenceDavid Johnston stated in media interviews that the government was considering acquiring F-35B fighters for the Canberra '​s, and Prime Minister Tony Abbott has instructed 2015 Defence White Paper planners to consider the option of embarking F-35B squadrons aboard the two ships.[506][507][508] Supporters of the idea claim that providing fixed-wing support to amphibious operations maximises aircraft capability, and the presence of a ski-jump ramp inherited from the original design means that the vessels are better suited to STOVL operations than equivalent ships with flat flight decks.[509] Opponents to the idea counter that embarking enough F-35Bs to be effective requires abandoning the ships' amphibious capability and would make the pseudo-carriers more valuable targets, modifications would be required to make the flight deck capable of handling vertical-landing thrust and to increase fuel and ordnance capacity for sustained operations, and that the F-35B project itself has been the most expensive and most problematic of the Joint Strike Fighter variants.[510][511][512]

The U.S Marine Corps plans to disperse its F-35Bs among forward deployed bases to enhance survivability while remaining close to a battlespace, similar to RAF Harrier deployment late in the Cold War which relied on the use of off-base locations that offered short runways, shelter, and concealment. Known as distributed STOVL operations (DSO), Marine F-35Bs would sustain operations from temporary bases in allied territory within the range of hostile ballistic and cruise missiles, but be moved between temporary locations inside the enemy's 24-48 hour targeting cycle. This strategy accounts for the F-35B's short range, the shortest of the three variants, with mobile forward arming and refueling points (M-Farps) accommodating KC-130 and MV-22 Osprey aircraft to rearm and refuel the jets, as well as littoral areas for sea links of mobile distribution sites on land. M-Farps could be based on small airfields, multi-lane roads, or damaged main bases, while F-35Bs would return to U.S. Navy ships, rear-area U.S. Air Force bases, or friendly carriers for scheduled maintenance; metal planking would be needed to protect unprepared roads from the F-35B's engine exhaust, which would be moved between sites by helicopters, and the Marines are studying lighter and more heat-resistant products.[513]

Compared to the F-35A, the F-35C carrier variant features larger wings with foldable wingtip sections, larger wing and tail control surfaces for improved low-speed control, stronger landing gear for the stresses of carrier arrested landings, a twin-wheel nose gear, and a stronger tailhook for use with carrier arrestor cables. The larger wing area allows for decreased landing speed while increasing both range and payload.

The United States Navy intends to buy 480 F-35Cs to replace the F/A-18A, B, C, and D Hornets and complement the Super Hornet fleet.[514] On 27 June 2007, the F-35C completed its Air System Critical Design Review (CDR), allowing the production of the first two functional prototypes.[515] The C variant was expected to be available beginning in 2014.[516] The first F-35C was rolled out on 29 July 2009.[517] The United States Marine Corps will also purchase 80 F-35Cs, enough for five squadrons, for use with navy carrier air wings in a joint service agreement signed on 14 March 2011.[429][430] A recent 2014 document stated that the USMC will also have 4 squadrons of F-35Cs with 10 aircraft per squadron for the Marine Corps' contribution to U.S. Navy carrier air wings.[518]

On 6 November 2010, the first F-35C arrived at Naval Air Station Patuxent River. The replacement engines for at-sea repair are too large to be transported by current underway replenishment systems.[519] In 2011, the F-35Cs were grounded for six days after a software bug was found that could have prevented the control surfaces from being used during flight.[520] On 27 July 2011, the F-35C test aircraft CF-3 completed its first steam catapult launch during a test flight in Naval Air Engineering Station Lakehurst; the TC-13 Mod 2 test steam catapult, representative of current fleet technology, was used. In addition to catapult launches at varying power levels, a three-week test plan included dual-aircraft jet blast deflector testing and catapult launches using a degraded catapult configuration to measure the effects of steam ingestion on the aircraft.[521]

On 13 August 2011, the F-35 successfully completed jet blast deflector (JBD) testing at Lakehurst. F-35C test aircraft CF-1 along with an F/A-18E tested a combined JBD cooling panel configuration. The tests measured temperature, pressure, sound level, velocity, and other environmental data; the JBD model will enable the operation of all carrier aircraft, including the F-35C. Further carrier suitability testing continued in preparation for initial ship trials in 2013.[522] On 18 November 2011, the U.S. Navy used its new Electromagnetic Aircraft Launch System (EMALS) to launch an F-35C into the air for the first time.[523]

In February 2014, Lockheed said the F-35C was on schedule for sea trials after the tailhook was redesigned. The new tailhook has a different shape to better catch arresting wires. Testing on land achieved 36 successful landings. Sea trials are scheduled for October 2014.[527]

On 3 November 2014, an F-35C of VX-23, one of the Navy's flight test units, made its first landing on an aircraft carrier when it recovered aboard USS Nimitz; this started a 2 week deployment of a pair of aircraft for the initial at sea Development Testing I or DTI, the first of three at sea tests planned for the F-35C.[528][529] The initial deployment was completed on November 14.[530]

The U.S. Navy may use the F-35C as part of its UCLASS effort to operate a carrier-based unmanned aerial vehicle. Though it has been suggested that the UCLASS could carry air-to-air weapons, an unmanned aircraft lacks situational awareness and is more vulnerable to electronic countermeasures than manned aircraft, and autonomy for deploying lethal weapons is not under development. With the F-35C as the center of a network of naval systems, it could feed information to the UCLASS and order it to fire on a certain target. Large numbers of F-35Cs operating in contested environments can generate a clear picture of the battlespace, and share it with unmanned assets that can be directed to attack.[531]

The F-35I is an F-35A with Israeli modifications. A senior Israel Air Force official stated "the aircraft will be designated F-35I, as there will be unique Israeli features installed in them". Despite an initial refusal to allow such modifications, the U.S. has agreed to let Israel integrate its own electronic warfare systems, such as sensors and countermeasures, into the aircraft. The main computer will have a plug-and-play feature to allow add-on Israeli electronics to be used; proposed systems include an external jamming pod, and new air-to-air missiles and guided bombs in the internal weapon bays.[532][533] Israeli pilots are scheduled to start F-35 training in December 2016 at Eglin AFB Florida with the first squadron activated about a year later.[534]

Israel Aerospace Industries (IAI) has considered playing a role in the development of a proposed two-seat F-35; an IAI executive stated: "There is a known demand for two seats not only from Israel but from other air forces."[535] IAI plans to produce conformal fuel tanks.[536] A senior IAF official stated that elements of the F-35's stealth may be overcome in 5 to 10 years, while the aircraft will be in service for 30 to 40 years, which is why Israel insisted on installing their own electronic warfare systems: "The basic F-35 design is OK. We can make do with adding integrated software."[537] Israel is interested in purchasing up to 75 F-35s.[538]

The Canadian CF-35 is a proposed variant that would differ from the F-35A through the addition of a drogue parachute and may include an F-35B/C-style refueling probe.[539] Norway may also use the drag chute option, as they also have icy runways.[285] Norway will be the first country to adopt the drag chute pod.[540] In 2012, it was revealed that the CF-35 would employ the same boom refueling system as the F-35A.[541] One alternative proposal would have been the adoption of the F-35C for its probe refueling and lower landing speed; the Parliamentary Budget Officer's report cited the F-35C's limited performance and payload as being too high a price to pay.[542]

On 23 June 2014, an F-35A preparing to take off on a training flight at Eglin Air Force Base experienced a fire in the engine area. The pilot escaped unharmed. The accident caused all training to be halted on 25 June, and all flights halted on 3 July.[422][423][424] During the incident investigation, engine parts from the burned aircraft were discovered on the runway, indicating it was a substantial engine failure.[565] The fleet was returned to flight on 15 July with restrictions in the flight envelope.[425] Preliminary findings suggests that excessive rubbing of the engine fan blades created increased stress and wear and eventually resulted in catastrophic failure of the fan.[566]

Hardpoints: 6 × external pylons on wings with a capacity of 15,000 lb (6,800 kg)[257][261] and two internal bays with two pylons with a capacity of 3,000 (1,360 kg)[257] for a total weapons payload of 18,000 lb (8,100 kg)[241] and provisions to carry combinations of:

^Quote: "The F-35 Lightning II will carry on the legacy of two of the greatest and most capable fighter aircraft of all time. Just as the P-38 and the British Lightning were at the top of their class during their day, the F-35 will redefine multi-role fighter capability in the 21st century." Ralph D. Heath, president of Lockheed Martin Aeronautics Co.[27]

^Quote: "The F-35A, with an air-to-air mission takeoff weight of 49,540 lb."[240]

^Quote: "Brigadier Davis was more forthright in his comments to media in Canberra, saying the ‘Raptor’ lacks some of the key sensors and the enhanced man-machine interface of the F-35."[339]